The present invention relates to a process for the manufacture of a foundry core or mould, in which process a composition comprising a granular filler, a synthetic resin which cures under the action of an acid, and a desensitized ketone peroxide composition is formed into the desired foundry core or mould and treated with sulphur dioxide.
A process of the type indicated above is known from U.S. Pat. No. 3,879,339. Such a process is based on the principle of sulphuric acid being formed in situ in the composition, causing a very rapid curing of the resin, the sulphur dioxide being converted into sulphuric acid in the presence of an oxidizing agent and mere traces of water. Essential in such process is that in such a way there will be no intermediate formation of sulphur dioxide, the curing action of which is unduly violent and unselective.
The above-mentioned process is used on a large scale. A ketone peroxide generally is used, as the oxidizing agent, more particularly the methyl ethyl ketone peroxide mentioned in Example 1 of U.S. Pat. No. 3,879,339.
The transport and storage of ketone peroxides in their pure state is forbidden by law in view of the risk of decomposition and the ensuing explosion hazards. Such a drawback is generally met by incorporating the ketone peroxide into a desensitizing agent. Provided that a proper desensitizing agent is chosen, there will no longer be any premature or undesirable decomposition of the ketone peroxide, or only to such a small degree that in actual practice it does not present any real danger.
The most commonly used desensitizing agents are the dialkyl esters of phthalic acid, more particularly dimethyl phthalate and diisobutyl phthalate. However, the use in the present process of ketone peroxide compositions desensitized with those agents would lead to serious problems. For, in the manufacture of castings, the foundry cores and moulds are exposed to a temperature in the range of 700.degree. to 1200.degree. C. At such high temperatures the phthalic esters will decompose, attended with the production of smoke, which not only obstructs visibility in the foundry, but also irritates the mucous membranes and the eyes of the people that are present there.
The present invention not only has for its object to find a suitable desensitizing agent for ketone peroxides as will not cause the formation of bothersome decomposition products during the use of foundry cores and moulds, but also to find a ketone peroxide composition resulting in good curing of the foundry cores and moulds.